#include<cstdio>
#include<algorithm>
using namespace std;
bool v[2000002];
int i,j,x,n;
int main ()
{
    freopen ("ciur.in","r",stdin);
    freopen ("ciur.out","w",stdout);
    scanf ("%d",&n);
    v[1]=true;x=1;
    for(i=3;i<=n;i+=2)
    if(v[i]==false)
	{
        for(j=i;j<=n/i;++j) v[j]=true;
    }
    for (i=3;i<=n;i+=2) {if (v[i]==false) ++x;}
    printf ("%d",x);
    return 0;
}